What is MCP?

Model Context Protocol (MCP) = Standardized way for LLMs to discover and call your external tools/data.

No more custom integrations. One protocol works everywhere.

MCP = 3 Layers

LLM/App ← Host → Client ← Protocol → Server (YOUR CODE)

1. Server (You write this)

# YOUR Python/Node.js server
from fastmcp import FastMCP

mcp = FastMCP("inventory-server")

@mcp.tool()
def check_stock(item_id: str) -> dict:
    return {"in_stock": True, "quantity": 42}

1. Client (MCP host manages)
   • Discovers available tools (tools/list)
   • Calls tools with validated params
   • Returns structured results
2. Host (Claude Desktop, Open WebUI, VS Code)
   • Wires LLM ↔ MCP Client
   • Handles conversation flow

The MCP Handshake (3 Steps)

1. Client → Server: “initialize” + capabilities
2. Server → Client: “tools/list” + schemas
3. Client → Server: “tools/call” → {“result”: …}

JSON example:

// Step 2: Server advertises tools
{
  "tools": [{
    "name": "check_stock",
    "inputSchema": {
      "type": "object",
      "properties": {"item_id": {"type": "string"}}
    }
  }]
}

// Step 3: Client calls tool
{"method": "tools/call", "params": {"name": "check_stock", "arguments": {"item_id": "SKU123"}}}

Real Flow Example

User: “Is iPhone 16 in stock?”

1. LLM → Host: “Need to call check_stock(‘iPhone16’)”
2. Host → Client → Server: tools/call
3. Server → DB → “Yes, 5 units”
4. LLM: “Yes, iPhone 16 is in stock (5 units left)”

Python vs Node.js

Python (FastMCP):

@mcp.tool()
def get_weather(city: str) -> str:
    return f"Weather in {city}: Sunny ☀️"

Node.js (TypeScript):

const mcp = new MCP('weather-server');
mcp.tool('get_weather', async (city: string) => {
  return `Weather in ${city}: Sunny ☀️`;
});

Why This Architecture Wins

• Self‑describing – Server advertises schemas, no docs needed
• Type‑safe – JSON Schema validation before calling
• Streaming – Large results stream back incrementally
• Local – Stdio/HTTP, no cloud required

Call‑to‑Action

“Now you know WHAT MCP is. Next: WHEN do hallucinations happen most?”

References

• FastMCP (Python) https://github.com/jlowin/fastmcp
• MCP Spec - Handshake https://modelcontextprotocol.io/docs/protocol
• FastMCP Node.js https://github.com/fastmcp/node-mcp